1. Field of the Invention
The present invention relates to an angle detecting apparatus using a line-type passive range-finding device, and to a projector having the same.
2. Description of Related Art
In a conventional projector, such as a liquid-crystal or DLP projector, there is a type of distortion known as keystone distortion which appears as a distorted shape of an image caused by an improper positional relationship between the projector and the screen. In keystone distortion, one side of the projected image is typically larger than an opposite side.
There are generally two techniques used for correcting keystone distortion, including an electric correction method in which an image generated by a video circuit is projected with a keystone distortion reverse to that of the projected image, and an optical correction method in which the inclination of a condensing lens of a projection optical system within the projector is adjusted without correcting an image generated in the video circuit.
Descriptions of the foregoing techniques for automatically correcting keystone distortion may be found, for example, in JP-A-2000-122617, JP-A-2001-339671 and JP-A-2002-62842, each of which is incorporated herein by reference.
For example, in the technique described in JP-A-2000-122617 distances to the screen are detected by two active-type range-finding sensors provided at different positions in a front surface of a liquid-crystal projector. On the basis of two detected distances and a distance between the two range-finding sensors, an inclination angle of the liquid-crystal projector relative to the screen is calculated. On the basis of this inclination angle, keystone distortion is corrected by the method mentioned above.
In the technique described in JP-A-2001-339671, an angle sensor circuit, such as gyro, is provided on a projector or a screen. On the basis of angle information obtained from such circuit, correction is made for a horizontal (left-right) keystone distortion, vertical (up-down) keystone distortion or combined horizontal-and-vertical keystone distortion.
The technique described in JP-A-2002-62842 uses a camera to detect a position and an inclination of a screen. The screen image taken by the camera is image-processed in a screen-position detecting section to thereby detect a screen position and inclination. Depending upon the detected position and inclination of the screen, a keystone distortion is corrected.